Line fault at the outlet -- do I need an electrician?

Yesterday, I got a Panamax, Max 1500 surge protector and line conditioner. (I got a very good deal on it, and am just trying it out.)

I plugged it into an outlet I've been using for a while and one of the red lights on the front lit up saying "line fault." (I'm not sure how this is different from a "ground fault." Maybe it's the same.) The Panamax does not do this with other outlets in the room. They seem ok.

So, I know this means that the outlet is improperly wired. My question is, might this be a simple thing to check and/or fix? Any suggestions most appreciated. It's the only outlet I can use to have my audio set up where I usually have it. Now is not an optimal time to call an electrician. If this is a big problem, I'll try out my gear somewhere else in the room, but if I can fix this without too much expertise, that would be ideal.
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Maybe the terminology is messing me up.

I have one panel in the house.

At the top, is the master on/off. Below are the breakers. I thought that's what you meant by subpanel. It is not a separate panel, in the sense that it is not another separate metal rectangle. There is one metal rectangle.

The subpanel contains, maybe, 30 breakers.
I followed a bunch of wires out of the box (9, 10?) and the orange one split off to the side of the house where I presume it is feeding the circuits/branch I mentioned.

It seems to me that someone used a 30 amp cable to feed two 15 amp circuits. There must be a junction box where the orange cable branches off to two 15 amp cables. You should get an electrician to check it out. You are better off playin' it safe!
A subpanel is a panel fed from another panel.

Like in my old house I had a 200 A main panel, but a sub panel in my workshop. The physical size isn’t the determining factor. What makes a sub panel a subpanel is that there’s another breaker in the house which controls all power to it.

The 200A main panel (techincally service panel) fed a subpanel via a 60 AMP breaker. That subpanel had 4 other breakers.